1. Field of the Invention
The present invention relates generally to valve actuating mechanisms for engines and, more particularly, to a dual feed hydraulic lash adjuster for a valve actuating mechanism for an internal combustion engine.
2. Description of the Related Art
It is known to provide valve actuating mechanisms to open and close valves of an engine such as an internal combustion engine. These valve actuating mechanisms may be of a finger follower type including a finger follower having a pallet or web engaging a stem of the valve and a dome socket engaging a rounded end of a hydraulic lash adjuster (HLA) supported by a cylinder head of the engine. The dome socket is known to have a dome with a concave recess or socket therein. Typically, a circular opening or orifice is provided in the dome for spraying hydraulic fluid supplied by the HLA from the socket into a camshaft compartment for lubricating a cam and cam follower and associated components of the valve actuating mechanism.
Hydraulic lash adjusters for variable lift valve actuating mechanisms for internal combustion engines are well known. Typically, the hydraulic lash adjuster (HLA) is disposed on an engine block of the engine. The HLA generally comprises a slidable plunger that may be hydraulically extended to take up mechanical lash in a valve train for the engine. In an example where a valve lift change is accomplished by increasing fluid pressure to the associated variable lift valve actuating mechanism, the HLA is supplied with low-pressure engine fluid for conventional lubrication and lash adjustment. When a valve lift change is desired, fluid pressure in the HLA is increased, and high-pressure fluid flows through the same circuit in the HLA to actuate the variable lift valve actuating mechanism. To reverse the change, the fluid pressure is again reduced.
A problem exists in some conventional HLA assemblies having a single fluid feed wherein the hydraulic fluid pressure is varied between the two modes. Because a minimum lash-adjusting hydraulic fluid pressure is present in the HLA at all times, the minimum required switching pressure must include the HLA minimum pressure. That is, the minimum required switching pressure must be higher than in other known systems wherein the lash adjuster and the switching element are independently supplied. Thus, providing dual independent fluid supply to a hydraulic lash adjuster represents an advance in the art.
U.S. Pat. No. 7,047,925 to Hendriksma discloses a dual feed hydraulic lash adjuster. In this patent, a dual feed hydraulic lash adjuster (HLA) for use in an internal combustion engine includes a hollow body and a plunger assembly disposed in a bore of the engine. A one-piece plunger body includes a first chamber for forming a low-pressure fluid reservoir and receiving a lash adjustment mechanism, and a second chamber open at one end and partially closed hemispherically for supporting a rocker arm and providing valve deactivating fluid thereto for an auxiliary valve actuation system. The first and second chambers are separated by a transverse web, optionally having a small-diameter passage therethrough for air evacuation.
The above-described patented dual feed hydraulic lash adjuster suffers from the disadvantage that there is no separate fluid pressure separator. Another disadvantage of the dual feed hydraulic lash adjuster is that there is only a fixed web between chambers of a plunger assembly, which is undesired. A further disadvantage of the dual feed hydraulic lash adjuster is that it has a one-piece plunger body, which is undesired.
Therefore, it is desirable to provide a new dual feed hydraulic lash adjuster in a valve actuating mechanism for an internal combustion engine. It is also desirable to provide a dual feed hydraulic lash adjuster that has a separate fluid pressure separator for the hydraulic fluid. It is further desirable to provide a dual feed hydraulic lash adjuster with separation between the fluid feeds for lubrication that optionally provides air evacuation. Thus, there is a need in the art to provide a dual feed hydraulic lash adjuster in a valve actuating mechanism for an internal combustion engine that meets at least one of these desires.